Check your vacuum hoses, especially for the idle control valve, as well as the valve itself. This is often the hidden culprit behind a poor idle and hard start. The oxygen sensor could also need replacing. Good luck and let us know what it was.

As for what the OVP does, click on blue and yellow D.I.Y. button at the top of this page and scoll down until you see the section on "Evaluating Electronic Engine Contols". About midway through that artcile is an explanation of the role and purpose of the OVP. Hope this helps.